1. Field of the Invention
This invention is directed to solid polyolefin compositions containing a foaming agent which ordinarily forms foam in alkaline solution. More particularly, the invention is concerned with solid polypropylene containing a foaming agent and an antifoaming amount of a barium compound which reacts with or forms water insoluble soaps with the foaming agent. In its more specific aspects, the invention is directed to solid polyolefins containing a stearate radical and a barium compound which forms a water insoluble soap with the stearate radical.
2. Description of the Prior Art
It has been known heretofore to add fatty acids and fatty acid compounds to solid polymers of alpha monoolefins such as polyethylene and polypropylene. It has been known to add stearates and stearic acid to such polymers. Furthermore, it has been known to add barium compounds such as barium sulphate, barium oxide, and the like to plastics containing fatty acids. These filled polyolefins, however, were used as radiation shields and insulating materials.
It has not been known heretofore that stearates and/or stearic acid added to polymers of alpha monoolefins having 2 to 8 carbon atoms in the molecule when used as contacting means or packing rings and the like in alkaline solutions tend to form foam in the alkaline solution by the leaching out of the stearate radical or stearic acid by the alkaline solution with resultant foaming on using the alkaline solution to remove acid gases. In the present invention this problem is solved by including a barium compound in with the polyolefin in an amount sufficient to form a water insoluble soap with the leached stearate radical and thereby suppress the foaming. For example, the polypropylene packings rings for the aqueous alkaline solution such as hot potassium carbonate solution extraction and recovery of CO.sub.2 and H.sub.2 S extraction towers have given rise to an extreme foaming problem. The problem has been traced to the formation of surface active agents (primarily potassium stearate) in the carbonate solution. The stearate radical comes from the stearates (Na, K, Ca, Zn, Mg.) added to the polyolefin to serve as mold release and/or neutralizing agents. Glyceryl monostearate may sometimes be added to the resin. Stearic acid in resins such as polyolefins results from neutralization of acid residues in the resin or polyolefin. These soaps stabilize the foams generated as the CO.sub.2 and H.sub.2 S is regenerated from the alkaline solution by heating and the towers spill liquid over into the gas recovery system. Many salts capable of imparting hardness to water will suppress foaming. These include water soluble compounds of calcium, magnesium and barium. However, a basic form of these elements would not only serve to impart hardness to the carbonate solution but would also serve to reduce the availability of the stearate ion if present in the polymer itself. of these possibilities only barium hydroxide and barium oxide have the basic properties and water solubility characteristics to serve in this capacity. Thus, they are the preferred material to incorporate into polypropylene and the like used for the molding of packing rings and other articles of manufacture where foaming occurs due to carbonate solution.
Our invention is directed to the encapsulation of 0.01 to 1.0% of barium oxide or hydroxide or other barium components, which form water insoluble soaps, into the injection molding resin used to manufacture packing rings or other forms of plastic materials which are to function in basic lithium, sodium or potassium solutions or other alkaline solutions such as amines as illustrated by diethanol amine where foaming is a problem. Such encapsulated barium compounds may be introduced through a concentrated masterbatch dry blend technique or may be introduced as the pure pulverized or powdered or finely divided form of the basic compound directly into the resin.
The following prior art was considered in connection with this invention:
U.S. Patents ______________________________________ 3,133,894 3,296,163 3,404,104 Foreign Patents ______________________________________ German 1,944,873 German 2,032,313 French 1,438,783 German Appl. 2,105,859 Canadian 599,694 Canadian 666,668 ______________________________________